A Few Specs on the Varo Er:Cr:Glass laser

pooua_at_aol.com
Date: 02/08/05 

Date: 7 Feb 2005 23:46:06 -0800

Sam,

I looked through my diary entries for 1993-1994 for details on the
Cr:Er:Glass eyesafe laser range-finder that I used to assemble for IMO
Varo.

Laser rod: My diary refers to the rod as Cu:Er:Yb:Glass, that is, with
copper and no chromium. That was unofficially what we had; I believe
the official information was that the rod was a Cr:Er:Glass laser.
Specific engineering details were not considered necessary for floor
techs, and the engineers were loath to give us that information (in
fact, they pretty much considered us an inferior life form). I got the
chemical composition from a commercial book on lasers, rather than from
any internal publication. The physical dimensions are 0.118 inches in
diameter (tolerance: +0.001 inch -0.000 inch) by 2 inches long (I
measured the dimensions from some of the rods I used, but I don't
remember where I got the tolerance). The ends were flat polished.
Estimated cost of the rod was $700. I did not record the detail in my
diary, but I recall there were something like 5 layers of coating on
the ends of the rods.

Reflectors: Beryllium copper core, gold coat. The detail is not in my
diary, but I believe there was a layer of nickel between the core and
the coat. The tabs that fit into the end piece slots had to be under
0.018 inches thick, or they would be too thick to fit (of course, there
were two halves that fit together, so a slightly thick reflector half
could be paired with a slightly thin reflector half, as long as they
fit in the slots). We could file off the gold coat from the tabs, but
had to be careful to stop at the nickel layer. If the beryllum copper
core were exposed, the reflectors had to be rejected. Estimated cost of
the reflectors was about $350 a set.

O-rings: There were two sets of o-rings. One set fit over the ends of
the laser rod, and were made of Viton. The other set fit over the ends
of the flashlamp, and were made of silicon. As I mentioned previously,
the o-rings provided the greatest risk of contaminating the ends of the
laser rod during assembly. I vaguely recall that we could use a solvent
to clean the Viton o-rings, but it was pointless to attempt to clean
the silicon o-rings. I think we had to change our finger cots after
handling the silicon o-rings. At the microscopic level that we worked,
these materials are filthy. They were the dirtiest materials under our
flowhoods, excluding the human body.

Twice a day, we had to spend 10 minutes wiping down everything above
the floor with isopropyl alcohol and rags. The room was monitored
regularly to ensure that it had no more than 100 thousand particles per
cubic foot of air. The flowhoods had no more than 10 thousand particles
per cubic foot of air. We entered and exited the clean room via an
airlock, which had a large mat composed of sheets of adhesive-coated
plastic to pick loose dust, hair and dirt from the soles of our shoes.
It annoyed me that people constantly defeated the airlock by propping
both sets of doors open, which should have contaminated the clean room.
However, the man who measured the air said that we were still within
compliance.

"Photos of Varo Rangefinder Erbium Laser"
http://repairfaq.ece.drexel.edu/sam/laserpic/varopics.htm

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